Fire resistance wood-based boards, process for producing same and compositions useful therefor

Abstract

Aqueous solutions or slurries consisting essentially of water, ammonium hydrogen orthophosphate and urea wherein the amount of urea is from about one-half of the orthophosphate to about equal to the orthophosphate on a molar basis are useful in providing a fire-retardant coating on wood fibers when such fibers and a thermosetting resin are consolidated, under the simultaneous application of heat and pressure, to produce a panel having a density of at least 0.5 grams per cubic centimeter. The useful range of compositions thus contain a P:C atomic ratio of from about 1:1 to about 2:1. Such panels are improved by providing, prior to subjecting the fibers to heat and pressure, intimate contact between the fibers, the orthophosphate and urea composition and providing an amount of composition of at least 10% by weight of the fibers whereby upon the application of heat and pressure a chemical reaction occurs and a wood-based, fire-retardant panel having a Class II flame rating and improved structural properties is produced.

What is claimed is: 
     
       1. A process for preparing a fire resistant wall board comprising forming a mixture of wood fibers with about 1% to about 2% by weight of said fibers of a thermosetting resin and about 10% to about 20% by weight of said fibers of a fire retardant composition consisting essentially of an ammonium hydrogen phosphate salt and urea having a P:C atomic ratio of from about 1:1 to about 2:1 and thereafter consolidating said mixture by the simultaneous application of heat and pressure to form a wood-like panel having a density of greater than 0.5 grams/cc. 
     
     
       2. The process of claim 1 wherein said wood fibers have a moisture content of from about 6% to about 8% by weight and said mixture additionally includes from about 1% to about 2% of a paraffinic pressing aid. 
     
     
       3. The process of claim 1 wherein intimate contact is provided between said fibers and said fire retardant composition by spraying a solution or slurry of said fire retardant composition in a solvent or suspension media upon said fibers and removing a sufficient amount of said solvent or suspension media to achieve a residual water content of from about 6 to about 8% prior to consolidation. 
     
     
       4. The process of claim 1 wherein said intimate contact is provided by an aqueous solution of said fire retardant composition. 
     
     
       5. The process of claim 4 wherein said phosphate salt is diammonium hydrogen orthophosphate. 
     
     
       6. The process of claim 5 wherein said P:C ratio is from about 1.2:1 to 1.5:1. 
     
     
       7. The process of claim 6 wherein said aqueous solution has a salt and urea content of from about 25 to 75% by weight. 
     
     
       8. A process according to claim 4 wherein said fire retardant is from about 15 to about 20% by weight of said fibers.